There are three general types of engine drives for recreational boats namely, inboard, outboard, and inboard-outboard. "Inboard" means that the engine and its driving shaft and Other components are positioned entirely inside the boat. "Outboard" means that the engine and its driving components are mounted on the transom and hang outside the boat. "Inboard-outboard" means a combination of the other two, wherein the engine is inside the boat and the drive shaft and some other drive components overhang the transom as in the outboard type. Generally, the outboard design takes up less space inside the boat, and the propellers can be lifted out of the water to permit the boat to be kept in shallow waters. The inboard design generally is forward on larger sizes of boats that need not be used in shallow waters. The inboard-outboard attempts to employ the best of both other types, in that the engine is inboard but the propellers can be lifted so as to be navigable in shallow waters. Inboard-outboard designs have employed dual propeller systems.
There has been prior knowledge of dual propellers employed on large ocean-going vessels, but there has not been known any use of dual, counter-rotating closely spaced concentric propellers on small recreational boats, i.e., boats of about 20-80 feet in length. The principal designs of such small boats have been for outboard or inboard-outboard engines in order for the boat to navigate shallow waters. Designs of inboard engines have avoided the dual concentric propeller feature for a variety of reasons, although many such boats employ two engines, each driving a single separate propeller, thus being defined as dual propellers, although not concentric.
It is an object of this invention to provide a transmission to connect a single engine on a small recreational boat to two concentric counter-rotating propellers. It is another object of this invention to provide a transmission to drive two concentric counter-rotating propellers through a V-drive system wherein the output drive shaft of the engine and the drive shafts of the propellers are at an acute angle to each other. Still other objects will appear in the more detailed description which follows.